Buggy code:
public class Prefix implements CommandExecutor { PexChatUtils plugin ; public Prefix ( PexChatUtils plugin ) { } @ Override public boolean onCommand ( CommandSender sender , Command cmd , String string , String [ ] args ) { if ( sender instanceof Player ) { Player player = ( ( Player ) ( sender ) ) ; if ( ( args . length ) == 0 ) { player . sendMessage ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + "Correct<seq2seq4repair_space>Usage:<seq2seq4repair_space>//prefix<seq2seq4repair_space>[prefix]<seq2seq4repair_space>|<seq2seq4repair_space>//prefix<seq2seq4repair_space>[player]<seq2seq4repair_space>[prefix]" ) ) ; } else if ( ( args . length ) == 1 ) { if ( player . hasPermission ( "pexchatutils.prefix" ) ) { String prefix = args [ 0 ] ; if ( ! ( plugin . wordChecker . wordIsBanned ( prefix ) ) ) { <START_BUG> plugin . chat . setPlayerSuffix ( player , prefix ) ; <END_BUG> player . sendMessage ( ( ( ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + "Your<seq2seq4repair_space>prefix<seq2seq4repair_space>has<seq2seq4repair_space>been<seq2seq4repair_space>changed<seq2seq4repair_space>to<seq2seq4repair_space>" ) + ( ChatColor . translateAlternateColorCodes ( '&' , prefix ) ) ) + ( ChatColor . LIGHT_PURPLE ) ) + "." ) ) ; } else { player . sendMessage ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + "A<seq2seq4repair_space>word<seq2seq4repair_space>in<seq2seq4repair_space>that<seq2seq4repair_space>prefix<seq2seq4repair_space>is<seq2seq4repair_space>banned!" ) ) ; } } else { player . sendMessage ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + "You<seq2seq4repair_space>do<seq2seq4repair_space>not<seq2seq4repair_space>have<seq2seq4repair_space>permission<seq2seq4repair_space>to<seq2seq4repair_space>run<seq2seq4repair_space>this<seq2seq4repair_space>command!" ) ) ; } } else if ( ( args . length ) == 2 ) { if ( player . hasPermission ( "pexchatutils.prefix.others" ) ) { String otherPlayer = args [ 0 ] ; String prefix = args [ 1 ] ; Player otherPlayer1 = Bukkit . getPlayer ( otherPlayer ) ; if ( otherPlayer1 != null ) { plugin . chat . setPlayerPrefix ( otherPlayer1 , prefix ) ; player . sendMessage ( ( ( ( ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + otherPlayer ) + "'s<seq2seq4repair_space>prefix<seq2seq4repair_space>has<seq2seq4repair_space>been<seq2seq4repair_space>changed<seq2seq4repair_space>to<seq2seq4repair_space>" ) + ( ChatColor . translateAlternateColorCodes ( '&' , prefix ) ) ) + ( ChatColor . LIGHT_PURPLE ) ) + "." ) ) ; } else { player . sendMessage ( ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + otherPlayer ) + "<seq2seq4repair_space>is<seq2seq4repair_space>not<seq2seq4repair_space>online!" ) ) ; } } else { player . sendMessage ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + "You<seq2seq4repair_space>do<seq2seq4repair_space>not<seq2seq4repair_space>have<seq2seq4repair_space>permission<seq2seq4repair_space>to<seq2seq4repair_space>run<seq2seq4repair_space>this<seq2seq4repair_space>command!" ) ) ; } } else { player . sendMessage ( ( ( ( ( ( ( ( ( ChatColor . BLUE ) + "[" ) + ( ChatColor . LIGHT_PURPLE ) ) + "PexChatUtils" ) + ( ChatColor . BLUE ) ) + "]<seq2seq4repair_space>" ) + ( ChatColor . LIGHT_PURPLE ) ) + "Correct<seq2seq4repair_space>Usage:<seq2seq4repair_space>//prefix<seq2seq4repair_space>[prefix]<seq2seq4repair_space>|<seq2seq4repair_space>//prefix<seq2seq4repair_space>[player]<seq2seq4repair_space>[prefix]" ) ) ; } } else { plugin . logger . info ( "This<seq2seq4repair_space>command<seq2seq4repair_space>can<seq2seq4repair_space>only<seq2seq4repair_space>be<seq2seq4repair_space>run<seq2seq4repair_space>by<seq2seq4repair_space>a<seq2seq4repair_space>player!" ) ; } return false ; } }

Fix:
plugin . chat . setPlayerPrefix ( player , prefix ) ;